NATIONAL NATURAL LANDMARKS PROGRAM
Columbia Cascades Cluster
Big Southern Butte (18)
Cassia Silent City of Rocks (20)
Crater Rings (21)
Great Rift System (22)
Hell's Half Acre Lava Field (24)
Menan Buttes (26)
Niagara Springs (27)
Landmark Descriptions
The butte is composed of light-colored silicic volcanic rocks and stands nearly 760 meters above the low relief surface of the Eastern Snake River Plain. The site is an ecological "island" supporting vegetation such as lodgepole pine (Pinus contorta), aspen (Populus sp.), Douglas fir (Pseudotsuga menziesii), and manzanita (Arctostaphylos sp.) not common to this region.
The springs emanate from rhyolite lava flows of the Madison Plateau, which comprise one of the largest rhyolite lava fields in the United States. Big Springs is the only first magnitude spring in the United States that issues forth from rhyolitic lava flows.
Big Springs (19)
Cassia Silent City of Rocks (20)
Located in the Cotterrel Range of south central Idaho, the site contains monolithic landforms created by exfoliation processes on exposed massive granitic plutons. The site contains the best example of bornhardts in this region.
Crater Rings are two closely adjacent pit craters that provide one of the few examples of this type in the continental United States. The crater rings are larger than, but similar to, pit craters along Chain of Craters Road on the southeast flank of Kilauea Volcano, Hawaii.
The Great Rift System of the eastern Snake River Plain is a dramatic and outstanding example of tensional tectonic forces in the earth's crust. The site also has biological interest as an example of primary vegetation succession on very young lava flows.
The site contains the world's richest known deposits of Upper Pliocene age terrestrial fossils.
Hagerman Fauna Sites (23)
Hell's Half Acre Lava Field (24)
The lava field is an outstanding example of a single event, single process geologic feature that is fully preserved and fully exposed. Fractures, depressions, and small lava caves are common features on the flow, which otherwise has a fairly smooth surface.
Hobo Cedar Grove Botanical Area (25)
This landmark contains a grove of old growth western red cedar in near natural condition. Two communities are represented: mainly western red cedar (Thuja plicata) / Oregon boxwood (Pachistima myrsinites) on the uplands and western red cedar / ladyfern (Athyrium filix-femina) on the lowland portions of the site.
Hobo Cedar Grove Botanical Area (25)
The site is an outstanding example of a glassy tuff cone, which is found in only a few places in the world. The buttes are composed of small fragments of basaltic glass formed by sudden chilling of magma.
The site is one of a number of large spring sets where the Snake River Plain aquifer drains into the Snake River from the northern cliffs of its canyon. It is illustrative of the enormous volume of water transmitted through this aquifer.
The site provides perhaps the best view of the horizontally layered lavas that represent successive flows of the Columbia River Basalt. The Columbia River Basalt covers an area of some 518,000 square kilometers in Idaho, Washington, and Oregon. It represents one of the great lava extrusions of geologic time.
Sheep Rock (28)
